The present invention relates to a method of treating ammonia-comprising waste water, wherein in a first step ammonia-comprising waste water is subjected to a nitrification reaction treatment by using a nitrifying microorganism and by the addition of oxygen, yielding a solution comprising an oxidation product of ammonia, and in a second step the oxidation product of ammonia together with ammonia is converted into nitrogen, through the influence of a denitrifying microorganism.
Such a method is known from U.S. Pat. No. 5,078,884. The nitrate formed by the oxidation of ammonia is used as an oxidant to convert, under substantially anaerobic conditions and with the aid of a microorganism, still to be degraded ammonia which acts as electron donor. During this process nitrogen is formed which is discharged into the atmosphere.
The disadvantage of this method is that there is no reliable degradation of ammonia, as can be seen in (the right half of) FIG. 2 of said publication. This means that undesirable discharges into the surface water may take place. To prevent this, all kinds of investments such as control and measuring equipment would be required. Finally, this method involves the addition of lye (see reaction equation 5 of said publication), which must also be controlled.
The objective of the present invention is to improve the method according to the preamble and in particular to provide a cost-effective, more reliable method which requires no additives and partly because of that, is simpler from a control-technological point of view.
Surprisingly, this objective can be achieved by a method which is characterized in that by using bicarbonate-containing waste water which is substantially stripped of bicarbonate by the supply of air, and in the first step maintaining the pH at xe2x89xa67.2 by controlling the aeration, part of the ammonia present in the waste water is converted into nitrite, yielding a nitrite-containing solution, and in the second step the denitrifying microorganism uses the thus formed nitrite as oxidant for the remaining ammonia.
In this manner a method is provided offering considerable advantages, one of which being a substantially more self-regulatory nature. Moreover, the use of additives is avoided.
From the prior art a method is known, comprising a nitritification step in which ammonia is converted into nitrite. In a denitritification step the nitrite is converted into nitrogen while an organic carbon source is added as substrate for a denitritifying organism. As organic carbon source methanol is used. When said methanol is degraded, acid, formed during the nitritification step, is consumed, providing the pH control of the denitritification process. The disadvantage of this non-continuous method is that an additive is required and much control is required such as time control and substrate feed control. The total conversion of ammonia is not under all conditions satisfactory and is limited to at the most 90% and for this reason a subsequent treatment is often required.